As known, the most widely employed industrial process for the synthesis of phenol is that providing for the decomposition of cumene hydroperoxide. At this time, over 90% of the phenol produced in the world is synthesized by this route, which simultaneously yields a mole of acetone per mole of phenol produced in accordance with the following reaction:C6H5—C(Me)2—OOH→C6H5—OH+MeCOMe
The cumene hydroperoxide is prepared by oxidizing cumene with air in a liquid phase:C6H5—C(Me)2+O2→C6H5—C(Me)2—OOH
The main byproducts of this reaction are acetophenone, dimethylphenylcarbinol and formic acid.
The latter in particular has, because of its acidity, the capability of catalyzing a partial decomposition of the cumene hydroperoxide to phenol, which even if present in parts per million, blocks the further oxidation of cumene with the result that the reaction is interrupted at an unacceptably low percentage of conversion.
It is known that in order to neutralize the formic acid byproduct aqueous solutions of sodium salts with organic acids are introduced into the cumene mixture so as to buffer the reaction environment. An alternative employed for the same purpose was that of using the sodium salt of the same cumene hydroperoxide under anhydrous conditions (U.S. Pat. No. 3,171,860 in the name of F. Codignola). On the other hand, the process in current use provides for feeding the oxidation reactor with cumene and caustic soda in a concentrated aqueous solution, so as to maintain a pH of an adequately high level to prevent initiating the decomposition of the hydroperoxide.
All the processes of the known art have in common that they utilize bases with inorganic cations (typically sodium, potassium and ammonium). Despite the fact that the reaction mixture exiting the oxidation step is washed with water to remove the salts, the cumene hydroperoxide thus produced still contains a small yet uneliminable percentage of inorganic cations in addition to a residual percentage of water. The presence of such cations is particularly disadvantageous for performing the subsequent decomposing reaction to yield phenol and acetone, as it interferes with the functionality of the acidic resins which could effectively be employed as decomposing catalysts. This consideration has limited the choice of acidic catalysts to traditional inorganic acids, in particular to sulphuric acid. The strong inorganic acids such as sulfuric acid, however, involve considerable safety problems in usage and waste disposal condition.